Stable mineral oil compositions



3,007,873 Patented Nov. 7, 1961 This invention relates to improved lubricating oil compositions, and more particularly to mineral lubricating oil compositions which are resistant to oxidative deterioration under storage or use in equipment subjected to adverse operating conditions of temperature and pressure.

Lubricating oils such as mineral oils in the lubricating viscosity range tend to deteriorate and break down due to oxidation both in storage and during use, particularly at extremely high temperatures, such as above 400 F. and higher, resulting in the formation of undesirable products such as gums, sludges, resins, acidic products and other deleterious products which decrease the useful life of'the oil or render it useless Within a short period of time. Mineral oils of this type include aircraft, truck and automobile mineral lubricating oils, industrial oils such as gear oils, transformer oils, hydraulic oils and the like.

It is known that certain aromatic amines are useful as oxidation inhibitors for mineral oils. However, their application is limited because of their tendency to discolor mineral oils and form deposits, particularly at elevated temperatures. Other types of anti-oxidants such as alkyl phenols, such as diand trialkylphenols, e.g., 2,4- diamylphenol and 2,6-ditert-buty1-4-methylphenol are effective only in certain type of mineral oil and are oxidatively unstable at elevated temperatures.

It is an object of this invention to inhibit or prevent oxidation of mineral oil. Still another object is to inhibit or prevent deterioration, discoloration and deposit formation in mineral oil during storage and use over a wide temperature range, particularly at elevated temperatures. Other objects of the invention will be apparent from the following description of the invention.

It has now been discovered that various types of mineral lubricating oil including those which contain substantial amounts of aromatic (30% can be effectively stabilized even at temperatures above 400 F. without undesirable side efiects by addition thereto of small amounts (0.001- 2%, preferably 0.002-1% by weight) each of an oilsoluble aromatic amine having the Formula I RR NH, wherein the Rs are the same or different monoor diaromatic radicals, and an oil-soluble boron ester having the Formula II (RO) B, wherein at least one R is an aryl radical having attached thereto at least 1 and preferably 2 branched-chain alkyl radicals such as tert-alkyl groups and the other Rs are the same or different hydrocarbyl radicals such as alkyl, aryl, alkaryl, aralkyl or cycloalkyl radicals. Boron esters represented by Formula II which contain at least two tert-alkyl-phenol Rs are preferred. 0

The oil-soluble aromatic amines represented by Formula I include diphenyl, dinaphthyl, phenyl alphanaphthyl, phenyl beta-naphthyl amines and mixtures thereof.

The boron esters represented by Formula II (RO) B are compounds wherein at least one R is a branched chain alkyl radical such as a tert-alkylaryl radical, e.g., tert-butylphenyl, tert-amylphenyl, tert-octylphenyl, ditertbutylphenyl, ditert-amylphenyl, ditert-octylphenyl, methylter-t butylphenyl, methylditert butylphenyl, ditertbutylnaphthyl, tert-butylnaphthyl, 2 ethylexylphenyl, etc. Boron esters of this type which are particularly preferred are borate esters containing a ditert-alkylphenyl group in the molecule such as 2,6-ditert-butyl-4-methylphenyl di-nbutyl borate, 2,6-ditert-butylphenyl di-n-butyl borate, 2,6- ditert-buty1-4-methylpheny1 di-n-octylborate, 2,6-ditert- 2 butyl-4-methylphenyl diphenyl borate, Z-ethylhexylphenyl dibutyl borate and the like.

The additive combination of this invention effectively stabilizes a variety of petroleum lubricating stocks such as paraflinic, naphthenic and mixed base mineral oils having a viscosity range of from 50 SUS at F. to 250 SUS at 210 F. A typical oil is a refined mineral lubricating oil (X) having the following properties:

Pour point, F 29-31 Flash point, F. (COC) Min. 420 Viscosity SUS, 100 F 345-355 Unsulfonated residue Min. 98

Another typical oil (Y) is an Oklahoma neutral petroleum fraction having the following properties:

Specific gravity 0.876 Pour point, F +10 Viscosity at 100 F., cs 56.88 93.9 450 490 23.7

To illustrate the pronounced superiority of the additive combination in stabilizing and preventing oxidation of mineral oil, the following compositions were prepared and evaluated in a micro-oxidation test of the MIL-L- 7808 oxidation test under the following test condition: air flow of l liter/hour oxidizing agent, 400 F., solid metal catalyst (Ag, Ti, Cu, Mg, Fe), with the results as shown in Table I.

reali n EoE iIIIIIIII:III: Fire point, F Aromatics, percent Table I [Base=retined mineral lubricating oil X. Amount of inhlbitor=0.02M=

0.002 mole/100 g.]

Hours to Gain Due Inhibitor Absorb 1 To mlllirnole Inhibitor,

Og/g. oil Hrs.

(1) None 11 (2) Phenyl-alpha-naphthylamine 19 8 (3) Beta-beta-dinapl1thylami11e 17 6 (4) Diphenylamine 15 4 (5) 2,6-ditert-butyl-4-methyl-phenyl di-nbutyl borate 18 7 2 5 62 51 29 18 46 35 The unexpected results which the additive combinations of the present invention produce were further demonstrated when oil compositions shown in Table II were tested in the Dornte Oxidation Test described in the National Petroleum News, September 17, 1941, pages R-294-296, with the results as shown in Table II.

Table II [Base=refined mineral oil (X). Oonditinns=302 F., 1800 ml., On cat, time, min. Amount of inhibitor=0.0025 mole/100 g. oi1=0.025 M] Inhibitor Time (min) (2) Pllenyl-alpha-naphthylamine 8, 340 (5) 2,6-ditert-butylphenyl-4-rnethylphenyl di-n-butyl borate. 1, 043 (6) 2+5 22,500

Lubricating oil compositions of this invention such as 4 4. A mineral lubricating oil containing from about 0.001% to about 2% each of dinaphthylamine and 2,6- ditert-butylphenyl di-n-butyl borate.

5. A mineral lubricating oil containing from about 5 0.001% to about 2% each of dinaphthylamine and 2,6-

ditert-butyl-4-methylphenyl di-n-butyl borate.

References Cited in the file of this patent UNITED STATES PATENTS 2,410,652 Griffin et a1 Nov. 2, 1946 2,497,521 Trautman Feb. 14, 1950 2,813,830 Trautman Nov. 19, 1957 

1. A MINERAL LUBRICATING OIL CONTAINING FROM ABOUT 0.001% TO ABOUT 2% EACH OF AN ARYL AMINE OF THE GROUP CONSISTING OF PHENYL-ALPHA-NAPHTHYLAMINE AND DINAPHTHYLAMINE AND A BORATE OF THE GROUP CONSISTING OF 2,6-DITERTBUTYLPHENYL DI-N-BUTYL BORATE AND 2,6-DITERT-BUTYL-4METHYLPHENYL DI-N-BUTYL BORATE. 